Local Area Network – Wired LAN

1. Local Area Network – Wired
LAN
LAN is a computer network that is designed for a limited
geographical area such as building or campus.
In 1980 and 1990s several different type of LANs were used. All of
these LAN used a media –access method to solve the problem of
sharing the media. The Ethernet used the CSMA/CD approach. The
token ring, Token BUS, and FDDi used token passing approach.
Almost every LAN except Ethernet has disappeared from the market
place because Ethernet was able to update itself to meet the need of
time.

2. Wired LAN has six essential components to
function.
 Network Adapter : A network adapter is usually the only
component within a computer for interfacing or connecting
with a network. Typically, it is built on a printed circuit board
with jumpers that connect it with the computer’s
motherboard. A network adapter for wired networks has an
RJ-45 port that uses twisted or untwisted pair cable for
network connectivity.
 Network Medium
 Wired networks need cable. The most common form of cable
used in networks is called the "Unshielded Twisted Pair." I

3. Cable Connectors
In wired networks, the most common form of
connector is the RJ45. Every computer with
networking capabilities has an RJ45 port. This is
sometimes called a "network port" or an "Ethernet
port."
Power Supply
Both wired and wireless networks need a power
supply. A wireless network uses the current to
generate radio waves. A cabled network sends data
interpreted as an electronic pulse

4. Hub/Switch/Router – connecting devices
Software: is the intelligence that causes all of the
components to function together. The most popular
network software today uses what is known as the
TCP/IP protocol suite, or stack. The suite is
constructed from actual layers of software, where
each has its own function.

5. ETHERNET
 Ethernet is most widely used LAN Technology, enabling devices to
communicate with each other via a protocol -- a set of rules or common
network language. which is defined under IEEE standards 802.3. The
reason behind its wide usability is Ethernet is easy to understand,
implement, maintain and allows low cost network implementation.
 Engineers at Xerox first developed Ethernet in the 1970s. Ethernet initially
ran over coaxial cables, while a typical Ethernet LAN today uses special
grades of twisted pair cables or fiber optic cabling. Early Ethernet
connected multiple devices into network segments through hubs -- Layer
1 devices
 It usually transmits at 10 Mbps and relies on CSMA/CD to regulate traffic
on the main cable segment.


6. The Institute of Electrical and Electronics Engineers
Inc. (IEEE) specifies in the family of standards
called IEEE 802.3 that the Ethernet protocol touches
both Layer 1 -- the physical layer -- and Layer 2 --
the data link layer -- on the OSI network protocol
model

7.  In IEEE 802.3 Ethernet Data link layer is split into two sublayers:
 Bottom part: MAC
 The frame is called IEEE 802.3
 Handles framing, MAC addressing, Medium Access control
 Specific implementation for each LAN protocol
 Defines CSMA/CD as the access method for Ethernet LANs and Token passing method for Token Ring.
 Implemented in hardware
 Top part: LLC (Logical Link Control)
 The subframe is called IEEE 802.2
 Provides error and flow control if needed
 It makes the MAC sublayer transparent
 Allows interconnectivity between different LANs data link layers
 Used to multiplex multiple network layer protocols in the data link layer frame
 Implemented in software

8. Figure 13.1 IEEE standard for LANs

9. IEEE Project.
Project 802 is a set of networking standards and
procedures for implementing networks, and creating
network related equipment.
The IEEE (institute of Electrical and Electronics
Engineers) designed Project 802 and it became a
standard in 1983.
The project mostly covers physical media aspects of
networking, such as cabling, attachments, hardware
recommendations, and some logical networking
aspects as well.

10. A list of the 802 Networking Standards and
uses:
 802.1: Internetworking. Covers routers, bridging, switches, and
other internetworking communications standards and
equipment.
 802.2: Logical Link Control. Covers the properties and
standards of physical media interoperability, such as with
network interface cards, attachment and cabling media.
 802.3: Ethernet: Covers standards and specifications of
implementing Ethernet networks.
 802.4: Token Bus LAN: Covers forms of physical media that
work with the Token Bus Networking topology.
 802.5: Token Ring LAN: Covers forms of physical media that
work with the Token Ring Topology

11.  802.6: Metropolitan Area Networks: Covers the procedures
and implementation procedures for managing large networks.
 802.7: Broadband Technical Advisory Group: Covers
broadband networking media concepts and procedures.
 802.8: Fiber Optic Technical Advisory Group: Covers the
standards and procedures for Digital Optical networking.
 802.9: Integrated Voice and Data Networks: Covers the
procedures for integrating voice and data over networks.
 802.10: Network Security: Covers the standards and
procedures for securing networks logically (software level),
and physically (Hardware level).
 802.11: Wireless Networking: Covers the procedures,
specifications, and implementation of wireless networks.

12. Ethernet Evolution / Types of Ethernet

13. Standard Ethernet ( 10 Mbps)
All Ethernet connections are limited by the slowest
component, be that the hub, the Ethernet card or
the Ethernet cable. While 10Mbps Ethernet long
remained the standard for local-area networking
and wide-area networking, it was ultimately held
back by the type of cable it used. “Manchester
encoding” cable could only handle as many bits as
10 million per second, so as long as the cabling
standard remained the same, so would the
throughput on the network.

14. Ethernet Standards and Cable
Designation Supported
Media
Maximum
Segment
Length
Transfer Speed Topology
10Base-5 Coaxial 500m 10Mbps Bus
10Base-2 ThinCoaxial
(RG-58 A/U)
185m 10Mbps Bus
10Base-T Category3 or
above
unshielded
twisted-pair
(UTP)
100m 10Mbps Star,using
either simple
repeater hubs
or Ethernet
switches

15. Fast Ethernet
The Fast Ethernet standard (IEEE 802.3u) has
been established for Ethernet networks that
need higher transmission speeds. This
standard raises the Ethernet speed limit from
10 Mbps to 100 Mbps with only minimal
changes to the existing cable structure. Fast
Ethernet provides faster throughput for video,
multimedia, graphics, Internet surfing and
stronger error detection and correction.

16. 100Base-TX Category5 UTP /
STP
100m 100Mbps Star,using either
simple repeater
hubs or Ethernet
switches
100Base-FX Fiber-optic- two
strands of
multimode
62.5/125 fiber
412 meters
(Half-Duplex),
2000 m (full-
duplex)
100 Mbps, (200
Mb/s full-duplex
mode)
Star(often only
point-to-point)
100Base –T4 UTP 100 m 100 Star

17. Gigabit Ethernet
Gigabit Ethernet was developed to meet the need for faster
communication networks with applications such as multimedia
and Voice over IP (VoIP). Also known as “gigabit-Ethernet-
overcopper” or 1000Base-T, GigE is a version of Ethernet that
runs at speeds 10 times faster than 100Base-T. It is defined in
the IEEE 802.3 standard and is currently used as an enterprise
backbone. Existing Ethernet LANs with 10 and 100 Mbps cards
can feed into a Gigabit Ethernet backbone to interconnect
high performance switches, routers and servers.

18. 1000Base-SX Fiber-optic- two
strands of
multimode
62.5/125 fiber
260m 1Gbps Star,using
buffered
distributor hub
(or point-to-
point)
1000Base-LX Fiber-optic- two
strands of
multimode
62.5/125 fiber or
monomode fiber
440m
(multimode)
5000 m
(singlemode)
1Gbps Star,using
buffered
distributor hub
(or point-to-
point)
1000Base-CX Twinax,150-
Ohm-balanced,
shielded,
specialty cable
25m 1Gbps Star(or point-to-
point)
1000Base-T4 Category5 100m 1Gbps Star

19. Ethernet Frame / or Working

20.  Preamble: The first field of the 802.3 frame contains 7 bytes (56 bits)
of alternating 0s and 1s that alerts the receiving system to the coming
frame and enables it to synchronize its input timing.
 Start of frame delimiter (SFD) – This is a 1-Byte field which is always set
to 10101011. SFD indicates that upcoming bits are starting of frame,
which is destination address.
 Destination Address – This is 6-Byte field which contains the MAC
address of machine for which data is destined.
 Source Address – This is a 6-Byte field which contains the MAC
address of source machine. As Source Address is always an individual
address (Unicast), the least significant bit of first byte is always 0.

21.  type : a two byte value representing either the length of the
frame or the specific protocol type). Protocol can be IP, ARP,
OSPF.
 Data – This is the place where actual data is inserted, also
known as Payload. Both IP header and data will be inserted
here, if Internet Protocol is used over Ethernet. The
data present may be as long as 1500 Bytes. In case data
length is less than minimum length i.e. 46 bytes, then
0’s is added to meet the minimum possible length.
 Cyclic Redundancy Check (CRC) – CRC is 4 Byte field. This
field contains 32-bits hash code of data, which is generated
over Destination Address, Source Address, Length and Data
field. If the checksum computed by destination is not same
sent checksum value, data received is corrupted.

22. CSMA/CD Algorithm
 To understand how CSMA/CD works, it makes sense to break down
the individual components of the term:
 Carrier sense (CS): The carrier state detection makes sure that all
network participants check whether the medium is currently free –
only then does the protocol initiate data transmission
 Multiple access (MA): Several participants (computers connected to
the network) share a transmission medium
 Collision detection (CD): The collision detection is an extension of
the original protocol and regulates how to proceed in case data
packets happen to collide

23. In Ethernet network (IEEE 802.3), all network participants
usually meet on a common transmission medium – a
cable. This meeting must be regulated to avoid chaos
during data transmission, which could lead to data loss
or damage. CSMA/CD algorithm offers a method that
organizes data transmission properly.
In this method, a station monitors the medium after it
sends a frame to see if the transmission was successful. If
so, the station is finished. If, however, there is a collision,
the frame is sent again.

24. How CSMA/CD works?
 Step 1: Check if the sender is ready for transmitting data
packets.
 Step 2: Check if the transmission link is idle?
Sender has to keep on checking if the transmission
link/medium is idle. For this it continuously senses
transmissions from other nodes. Sender sends dummy data
on the link. If it does not receive any collision signal, this
means the link is idle at the moment. If it senses that the
carrier is free and there are no collisions, it sends the data.
Otherwise it refrains from sending data.

25.  Step 3: Transmit the data & check for collisions.
Sender transmits its data on the link. CSMA/CD does not use
‘acknowledgement’ system. It checks for the successful and
unsuccessful transmissions through collision signals. During
transmission, if collision signal is received by the node,
transmission is stopped. The station then transmits a jam
signal onto the link and waits for random time interval
it resends the frame. After some random time, it again
attempts to transfer the data and repeats above process
 Step 4: If no collision was detected in propagation, the
sender completes its frame transmission and resets the
counters.

28. IEEE 802.4 (Token Bus)
This standard, 802.4, describes a LAN called a token
bus. Physically, the token bus is a linear or tree -
shaped cable onto which the stations are attached.
Logically, the stations are organized into a ring, with
each station knowing the address of the station to
its “right” and “left”.

29.  Token Bus was a 4 Mbps Local Area Networking technology
created by IBM to connect their terminals to IBM mainframes.
Token bus utilized a copper coaxial cable to connect multiple
end stations (terminals, wokstations, shared printers etc.) to
the mainframe.
 The coaxial cable served as a common communication bus
and a token was created by the Token Bus protocol to
manage or 'arbitrate' access to the bus. Any station that holds
the token packet has permission to transmit data. The station
releases the token when it is done communicating

30. 

31.  MAC Sublayer Function
 • When the ring is initialized, stations are inserted into it
order of station address, from highest to lowest.
• Token passing is done from high to low address.
Whenever a station acquires the token, it can transmit
frames for a specific amount of time.
• If a station has no data, it passes the token immediately
upon receiving it.

33.  Preamble (PRE)- 1 bytes. The PRE is an alternating pattern of ones and
zeros that tells receiving stations that a frame is coming, and that provides a
means to synchronize the frame-reception portions of receiving physical
layers with the incoming bit stream.
 SDEL / EDEL - Starting Delimiter / Ending Delimiter. These fields are used to
mark the frame boundaries. Both of these fields contain analog encoding of
symbols other than 0s and 1s, so that they cannot occur accidentally in the
user data. As a result, no length field is needed.
 FC - Frame control field indicates whether the frame contains data or
control information
Destination address - Destination station address.
 Source address - Source station address.
 Data – The actual information that needs to be transferred. Its range is
between 0-8182 bytes.
 Checksum – This field is used to detect transmission errors.

34. IEEE 802.5 token ring
 Token Ring is a LAN protocol defined in the IEEE 802.5 where all
stations are connected in a ring and each station can directly hear
transmissions only from its immediate neighbor. Permission to
transmit is granted by a message (token) that circulates around the
ring.
 Token Ring as defined in IEEE 802.5 is originated from the IBM
Token Ring LAN technologies.
 A ring consists of a collection of ring interfaces connected by point-
to-point lines i.e. ring interface of one station is connected to the
ring interfaces of its left station as well as right station. Internally,
signals travel around the Communication network from one station
to the next in a ring.

35. Token Ring and IEEE802.5 are based on token passing
MAC protocol with ring topology. They resolve the
uncertainty by giving each station a turn on by one. Each
node takes turns sending the data; each station may
transmit data during its turn. The technique that
coordinates this turn mechanism is called Token passing;

36. Whenever a station wants to transmit a frame it inverts a
single bit of the 3-byte token which instantaneously
changes it into a normal data packet. Because there is only
one token, there can atmost be one transmission at a time.
Since the token rotates in the ring it is guarenteed that
every node gets the token with in some specified time. So
there is an upper bound on the time of waiting to grab the
token so that starvation is avoided.
There is also an upper limit of 250 on the number of nodes
in the network.

39.  SDEL / EDEL - Starting Delimiter / Ending Delimiter. Alerts arrival of a token / data /
control frame.
 AC - Access control field Contains the Priority fields.
 FC - Frame control field indicates whether the frame contains data or control
information Destination address - Destination station address.
 Source address - Source station address.
 Route information - The field with routing control, route descriptor and routing
type information.
 Information - The Information field may be LLC (logical link control) or MAC (Media
Access Control).
 FCS - Frame check sequence.
 Frame status - Contains bits that may be set on by the recipient of the frame to
signal recognition of the address and whether the frame was successfully copied.